1. Field of the Invention
The present invention relates to a print head of an ink-jet printer and a fabrication method thereof, and more particularly, to a monolithic bubble-ink jet print head and a fabrication method thereof, having an anti-curing-deformation part to prevent a nozzle plate or a chamber/nozzle plate from being abnormally deformed during ultraviolet (UV) curing or thermal hardening.
2. Description of the Related Art
Since an ink-jet printer is excellent in prevention of noise and in obtaining a high resolution, and it is also capable of performing color printing at a low cost, consumer demand for the ink-jet printer has been increased.
Also, with the development of the semiconductor technology, a fabrication technology of a print head, which is a main component of the ink-jet printer, has been actively developed during the past decade. As a result, a print head having about 300 injection nozzles and providing a resolution of 1,200 dpi is being used in a disposable ink cartridge.
FIGS. 1A and 1B schematically show a conventional print head 10 for an ink-jet printer.
Generally, ink is supplied from a back surface of a substrate 1 of the print head 10 to a front surface of the substrate 1 through an ink supply channel 2.
The ink supplied through the first ink supply channel 2 flows along restrictors 3 defined by a chamber wall or plate 9a and a nozzle plate 9b to reach ink chambers 4. The ink temporarily stagnating in the ink chambers 4 is instantly boiled by a heat generated from heaters 6 disposed under a protective layer 5, wherein the heaters 6 are connected to a contact pad 8 that is contacted to a lead terminal of an outer circuit to receive an electrical signal therefrom.
As a result, the ink generates an explosive bubble and, due to the bubble, some of the ink in the ink chambers 4 is discharged outwardly from the print head 10 through nozzles 7 formed above the ink chambers 4.
In such a print head 10, a chamber/nozzle plate 9 having the chamber plate 9a and the nozzle plate 9b, which are formed in a body or are formed in two different units, is an important factor that affects an ink flow, an injection pattern of the ink, an injection frequency, and the like. Accordingly, materials, shapes and fabrication methods of the chamber/nozzle plate 9 have been the subject of considerable research.
Current methods of fabricating the print head in relation to the chamber plate and the nozzle plate are an adhering method, i.e., separately fabricating a substrate and a nozzle plate, aligning and then adhering them to each other by utilizing a photosensitive high molecular weight thin layer, and a monolithic method directly forming a substrate and a nozzle plate in a body or in two different units on a substrate.
The adhering method may be classified into two types: a first type of separately fabricating only a nozzle plate, aligning and then adhering it on a substrate having a chamber plate made of polymer by utilizing an adhesive, and a second type of fabricating a nozzle plate and a chamber plate together, aligning and then adhering it on a substrate by utilizing an adhesive.
Generally, the fabrication method of the print head employing the monolithic method has the following advantages as compared with the adhering method.
First, there is no need for an adhesive, that is, a photosensitive high molecular weight thin layer that has to meet a particular condition is not required. Also, it is also not required to precisely align a nozzle plate and a substrate and adhere them to each other by utilizing the photosensitive high molecular thin weight layer, and equipment necessary to perform this work is also not required.
Secondly, a substrate, a chamber plate and a nozzle plate may be aligned more precisely as compared with the adhering method. Therefore, fabrication cost is reduced and productivity is increased by reducing the number of fabrication processes, and an advantage is achieved in that the print head no longer requires a precise alignment and a high resolution.
The following description sets forth a fabrication process of a general print head 10 according to a monolithic method that directly forms a chamber plate and a nozzle plate on a substrate.
First, as shown in FIG. 2A, a heater 6 and a protective layer 5 are formed on a silicone substrate 1.
Next, a preliminary ink supply channel 2′ that is used to form an ink supply channel 2 later is formed in a back surface of the substrate 1. At this time, a part of the substrate 1 at which the preliminary ink supply channel 2′ is formed is not completely removed and penetrated, but is left at a certain thickness.
After that, a positive photo resist is formed on the protective layer 5 of the substrate 1. The positive photo resist is patterned by a photolithography process that utilizes a photo mask (not shown). As a result, as shown in FIG. 2B, a positive photo resist mold 3′ of a sacrificial layer is formed on the protective layer 5. The positive photo resist mold 3′ provides a flow channel structure that includes restrictors 3 and ink chambers 4 that are removed through an etching process later. A thickness of the positive photo resist mold 3′ has a height substantially the same as the height of the restrictors 3 and the ink chambers 4 to be formed later.
After forming the positive photo resist mold 3′ on the protective layer 5, a whole surface of the substrate 1 is coated with a photosensitive epoxy resin as a negative photo resist.
After that, the negative photo resist is exposed to UV by using a photo mask (not shown) in which a shape of the nozzles 7 is patterned, and then a part of the chamber/nozzle plate 9, except for a part hardened by being exposed to the UV, is dissolved and removed by a developing liquid. As a result, as shown in FIG. 2C, a chamber/nozzle plate 9 having the nozzles 7 formed therethrough is obtained.
After the chamber/nozzle plate 9 is formed, as shown in FIG. 2D, the part of the silicon substrate 1, at which the preliminary ink supply channel 2′ is formed, is isotropically etched, so that an ink supply channel 2 is formed.
After that, as shown in FIG. 2E, the photo resist mold 3′ is dissolved and removed by a solvent. As a result, ink chambers 4 and restrictors 3 are formed in the chamber/nozzle plate 9.
After the formation of the chamber/nozzle plate 9, to enhance mechanical strength and corrosion resistance of the chamber/nozzle plate 9 and to adhere the chamber/nozzle plate 9 to the substrate 1 more closely, as well as to enhance endurance of the flow channel structure, a curing process applies the UV and heat to the chamber/nozzle plate 9 to increase a molecular weight, i.e., a cross linking density of the chamber/nozzle plate 9, with respect to the resultant substrate 1, and the fabrication of the print head 10 is finally completed.
Such a conventional monolithic method of fabricating the print head 10 has an advantage that the nozzle plate and the chamber plate are not separately formed, but are formed in a single body. However, the monolithic method of fabricating the print head 10 presents a problem that the chamber/nozzle plate 9 may be abnormally deformed due to curing conditions during the curing processing.
More specifically, if the curing processing is carried out at a relatively high temperature, the photosensitive epoxy resin of the chamber/nozzle plate 9 may reach the cross linking density in a short time, but the chamber/nozzle plate 9 may be abnormally deformed due to an increase in compressive stress applied thereto.
However, if the curing processing is carried out at a relatively low temperature, a time required for the photosensitive epoxy resin to reach the cross linking density is increased, lengthening the processing consumption time. Also, the compressive stress applied to the chamber/nozzle plate 9 may be decreased, but the chamber/nozzle plate 9 may still have abnormal deformation.
This abnormal deformation of the chamber/nozzle plate 9 generated during the curing process assumes a convex form 11 when the compressive stress is applied to a lower part of the nozzle plate 9b that is larger than an upper part thereof, as shown in FIG. 3A, whereas the chamber/nozzle plate 9 assumes a concave form of 11′ when the compressive stress is applied to the lower part of the nozzle plate 9b that is smaller than the upper part thereof, as shown in FIG. 4A.
Also, the deformation is generally generated at a region of the nozzles 7a and 7b in odd and even rows positioned at a center part (a center in a longitudinal direction of FIG. 1A) of the chamber/nozzle plate 9 that is larger than regions of the nozzles 7a and 7b that are located in the odd and even rows positioned at both edge parts of the chamber/nozzle plate 9.
Such an abnormal deformation of the chamber/nozzle plate 9 affects a quality in the image that is to be printed on a sheet of paper.
For example, when a vertical line is printed, the nozzles 7a in the odd row and the nozzles 7b in the even row jet ink alternately perform the printing operation. At this time, the print head 10 prints one vertical line when an alignment error between the nozzles 7a in the odd row and the nozzles 7b in the even row is within a tolerance limit.
That is, as is shown in FIG. 5B, when there is no abnormally deformed part in the chamber/nozzle plate 9, or when there is an abnormally deformed part in the chamber/nozzle plate 9, but it is positioned at the edge part of the chamber/nozzle plate 9 adhered to the substrate 1 to allow the alignment error between the nozzles 7a and 7b to be in the tolerance limit, the nozzles 7a and 7b print one vertical line, as shown in FIG. 5C.
However, as is shown in FIG. 3B, when the chamber/nozzle plate 9 has a part deformed in the convex form 11, since the nozzles 7a in the odd row and the nozzles 7b in the even row are misaligned with respect to one another at the deformed part of the chamber/nozzle plate 9, they print one line at an upper part and a lower part of the vertical line, but they print two lines at a center part of the vertical line providing a line that corresponds to the deformed part, as is shown in FIG. 3C.
Also, as is shown in FIG. 4B, when the chamber/nozzle plate 9 has a part deformed in the concave form 11′, since the nozzles 7a in the odd row and the nozzles 7b in the even row are misaligned with respect to one another at the deformed part of the chamber/nozzle plate 9, they print two lines at an upper part and a lower part of the vertical line that corresponds to the deformed part, as shown in FIG. 4C.
FIG. 6 is a schematic representation of a printing result in which vertical and horizontal lines are printed by a print head in which the chamber/nozzle plate 9 has the center part deformed in the convex form 11, as is shown in FIG. 3B. FIG. 6 shows that in the vertical lines, a portion printed by the nozzles 7a in the odd row and the nozzles 7b in the even row positioned at the edge part of the chamber/nozzle plate 9, results in one line, whereas a portion printed by the nozzles 7a in the odd row and the nozzles 7b in the even row positioned at the center part of the chamber/nozzle plate 9, results in two lines. To the contrary, it shows that in the horizontal lines, the portions printed by the nozzles 7a in the odd row and the nozzles 7b in the even row positioned at the edge part and the center part of the chamber/nozzle plate 9 result in one line.